14.2 Periapical, Bitewing & Occlusal Projections

14.2 Periapical, Bitewing & Occlusal Projections

Intraoral radiography provides the clinician with essential diagnostic views of the crowns, roots, pulp chambers, periodontal attachments, and alveolar bone. Depending on the clinical diagnostic objective, the dental assistant exposes three fundamental types of intraoral projections: periapical (PA) radiographs, bitewing (BWX) radiographs, and occlusal radiographs. Each projection demands meticulous receptor placement, precise horizontal and vertical angulation, and systematic quality assurance to ensure diagnostic efficacy while minimizing patient radiation exposure.

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The Full-Mouth Series (FMS / CMS / FMX)

A Full-Mouth Series (FMS)—also referred to as a Complete Mouth Series (CMS) or FMX—is a comprehensive set of intraoral radiographs that displays every tooth, crown, root, intervening contact area, and supporting alveolar bone in both the maxilla and mandible.

Clinical Composition of an Adult FMS

A standard adult FMS typically comprises 18 to 20 individual exposures, combining periapical and bitewing projections:

1. Anterior Periapicals (6 to 8 exposures): Imaged using narrow Size #1 receptors (or standard Size #2 receptors) oriented vertically. Vertical orientation is mandatory in the anterior region to accommodate the longer root lengths (particularly maxillary canines) and narrow dental arches. A typical series includes:
   • Maxillary central and lateral incisor projection (midline view or separate right/left views).
   • Maxillary right and left canine projections.
   • Mandibular central and lateral incisor projection (capturing all four incisors).
   • Mandibular right and left canine projections.
2. Posterior Periapicals (8 exposures): Imaged using standard Size #2 receptors oriented horizontally to accommodate the wider mesiodistal crowns and multi-rooted anatomy of posterior teeth:
   • Maxillary right premolar and molar projections.
   • Maxillary left premolar and molar projections.
   • Mandibular right premolar and molar projections.
   • Mandibular left premolar and molar projections.
3. Bitewing Projections (4 exposures): Imaged using Size #2 receptors:
   • Right premolar and molar bitewings.
   • Left premolar and molar bitewings.

Clinical Indications & ADA/FDA Selection Criteria

An FMS is never exposed on an arbitrary calendar schedule. In accordance with the ADA/FDA Dental Radiographic Examination Guidelines, intraoral radiographic series must be ordered only after a comprehensive clinical evaluation. Primary indications include:

• A new adult patient presenting with clinical evidence of generalized dental disease (multiple active carious lesions, extensive existing restorations, or generalized periodontitis).
• A comprehensive diagnostic baseline for full-mouth reconstruction, advanced prosthetic rehabilitation, or complex surgical treatment.
• Evaluation of a patient with extensive, severe periodontal destruction where crestal and apical structures cannot be visualized on localized radiographs.

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Periapical (PA) Radiographs: Diagnostic Criteria & Anatomy

The periapical radiograph derives its name from the Latin peri (around) and apex (terminal root tip). Its primary diagnostic mission is to evaluate the entire anatomical tooth and its immediate supporting periodontal tissues.

Stringent Diagnostic Quality Criteria

For a periapical radiograph to be considered clinically diagnostic, it must satisfy four mandatory criteria:

1. Full Coronal and Radicular Visualization: Must capture the entire anatomical crown, the full root length, and the pulp chamber without apex cutoff.
2. Periapical Alveolar Bone Margin: Must display a minimum of 2.0 to 3.0 mm of intact alveolar bone beyond the anatomical root apex. This surrounding zone of bone is essential for evaluating periapical health.
3. Open Interproximal Contacts: Contact areas between adjacent target teeth must not overlap horizontally, allowing assessment of proximal restorations and root proximity.
4. Absence of Technique Artifacts: Free of cone-cutting, elongation, foreshortening, bending distortion, motion unsharpness, or processing/digital errors.

Critical Anatomical & Pathological Features on Periapicals

• Lamina Dura: The continuous, thin, dense radiopaque cortical bone lining the tooth socket. Disruption or loss of the lamina dura at the apex is a primary radiographic indicator of periapical inflammation secondary to pulpal necrosis.
• Periodontal Ligament (PDL) Space: A thin, uniform radiolucent band (approximately 0.2 mm wide) located between the root cementum and lamina dura. Apical widening of the PDL space signifies early periapical periodontitis or traumatic occlusal loading.
• Periapical Pathologies: Detection of periapical radiolucencies (periapical abscess, granuloma, or radicular cyst) and periapical radiopacities (condensing osteitis, hypercementosis, cementoblastoma).
• Root Architecture: Visualizes root curvature (dilaceration), developmental anomalies, internal and external root resorption, root fractures following trauma, and root canal morphology prior to endodontic instrumentation.

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Bitewing (BWX) Radiographs: Caries Detection & Periodontal Crest Evaluation

The bitewing projection is the single most valuable radiographic view for detecting interproximal caries and assessing crestal alveolar bone height. The patient bites down on a central tab or wing, recording the coronal halves of both maxillary and mandibular arches on a single image.

Diagnostic Objectives & Angulation Rules

• Caries Detection: Evaluates early demineralization of interproximal enamel surfaces beneath the contact point, recurrent decay along proximal restorative margins, and occlusal caries penetrating the dentinoenamel junction (DEJ).
• Periodontal Bone Height: Displays the alveolar crest in relation to the cementoenamel junction (CEJ). In healthy periodontium, the crest of the alveolar bone resides 1.5 to 2.0 mm apical to the CEJ.
• Vertical Angulation (+10 Degrees): When performing bitewing radiographs, the vertical angulation of the PID must be set to +10 degrees (pointing slightly downward). This positive angulation serves two critical anatomical purposes:
  1. It compensates for the slight lingual inclination of maxillary posterior crowns.
  2. It compensates for the slight bending of the bite tab or sensor caused by tongue and palatal resistance when the patient occludes firmly.

Horizontal vs. Vertical Bitewings

In moderate-to-severe periodontitis, the alveolar bone recedes apically toward the middle and apical thirds of the roots. On a standard horizontal bitewing, the receded crest lies entirely below the lower border of the receptor, showing only empty air where the bone should be. Vertical bitewings are preferred for patients with significant bone loss because the vertical dimension provides the necessary vertical coverage to image the receded alveolar crest and root furcations while retaining open interproximal contacts.

Specific Quadrant Alignment for Bitewings

• Premolar Bitewing: Must capture the distal half of the mandibular canine, the first and second premolars, the first molar, and open contacts between the first and second premolars.
• Molar Bitewing: Must capture the distal half of the second premolar, the first, second, and third molars (if present), centered over the second molar with open contacts between the first and second molars.

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Occlusal Projections: Armamentarium & Anatomical Indications

The occlusal projection is an intraoral radiographic examination where the receptor is positioned on the occlusal plane between the biting surfaces of the maxillary and mandibular teeth. The patient gently closes their teeth together to hold the receptor like a sandwich.

Armamentarium & Receptor Sizes

• Adults: Utilizes large Size #4 receptors (measuring approximately 57 x 76 mm, often referred to as "sandwich film").
• Pediatric Patients: Utilizes standard Size #2 receptors placed horizontally between the arches.

Primary Clinical Indications

1. Locating Large Pathological Lesions: Retaining large cysts, ameloblastomas, odontogenic tumors, or extensive osteomyelitis lesions that exceed the boundaries of periapical sensors.
2. Salivary Gland Calculus (Sialolithiasis): Detecting radiopaque salivary stones within the submandibular duct (Wharton's duct) or sublingual gland tissues in the floor of the mouth.
3. Locating Impacted & Supernumerary Teeth: Determining the buccolingual position of impacted maxillary canines, impacted third molars, or midline supernumerary teeth (mesiodens).
4. Maxillofacial Trauma: Identifying fractures of the mandibular symphysis, body, or maxillary alveolar processes when extraoral imaging is unavailable.
5. Evaluating Cleft Palate: Visualizing bony defects of the hard palate in pediatric and cleft palate patients.
6. Patients Unable to Tolerate Periapicals: Young children, geriatric patients, or patients with severe trismus (inability to open the mouth) who cannot tolerate periapical bite blocks.

Key Occlusal Projection Techniques

• Maxillary Topographic Occlusal Projection:
  • Patient Position: Head upright with occlusal plane parallel to the floor; midsagittal plane perpendicular to the floor.
  • Central Ray Angulation: Directed at +65 degrees vertical angulation through the bridge of the nose, centered toward the middle of the #4 receptor.
  • Anatomy Displayed: Anterior palate, nasal septum, incisive foramen, and maxillary canine-to-canine region.
• Mandibular Cross-Sectional (True Occlusal) Projection:
  • Patient Position: Patient is reclined back, and the head is tipped backward so that the occlusal plane is oriented perpendicular to the floor.
  • Central Ray Angulation: Directed at 90 degrees to the receptor, entering through the soft tissue floor of the mouth approximately 1 inch below the chin.
  • Anatomy Displayed: Complete cross-section of the mandible, showing the buccal and lingual cortical plates, anterior teeth, and soft tissues of the floor of the mouth. This is the gold standard intraoral projection for detecting radiopaque sialoliths in Wharton's duct and diagnosing buccal-lingual cortical bone expansion.

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Radiographic Localization Techniques: The SLOB Rule

A conventional dental radiograph is a two-dimensional flat representation of a three-dimensional anatomical structure. It depicts vertical height and mesiodistal width, but lacks buccolingual depth. When a radiopaque object (such as an impacted canine, a broken endodontic instrument tip, a foreign body, or a supernumerary tooth) is detected on a radiograph, the clinician must determine whether it lies on the buccal (facial) or lingual (palatal) aspect.

The Buccal Object Rule (Clark's Rule / SLOB Rule)

In 1910, Charles Clark established the buccal object rule, widely memorized by the acronym SLOB: Same Lingual, Opposite Buccal.

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| The SLOB Rule (Same Lingual, Opposite Buccal):                                |
|                                                                                |
|  Radiograph 1 (Reference): Normal Horizontal Angulation                        |
|  Radiograph 2 (Shifted):   Tubehead Shifted Distally (or Mesially)            |
|                                                                                |
|  * IF Object moves in the SAME direction as the tubehead shift:                |
|    ===> Object is located on the LINGUAL (Palatal) aspect.                    |
|                                                                                |
|  * IF Object moves in the OPPOSITE direction to the tubehead shift:            |
|    ===> Object is located on the BUCCAL (Facial) aspect.                      |
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Clinical Execution Protocol

1. First Exposure (Reference Radiograph): Expose a standard periapical radiograph of the target region using standard horizontal and vertical angulation.
2. Second Exposure (Shifted Radiograph): Expose a second periapical radiograph of the same area, but intentionally shift the horizontal angulation of the tubehead mesially or distally (or shift vertical angulation superiorly or inferiorly).
3. Evaluation: Compare the movement of the unknown object relative to a known anatomical landmark (such as a root canal or tooth crown):
   • If the object appears to move in the same direction as the tubehead shift, the object is located on the lingual.
   • If the object appears to move in the opposite direction of the tubehead shift, the object is located on the buccal.

The Right-Angle Technique (Miller's Technique)

The right-angle technique uses two radiographs exposed at a 90-degree right angle to one another: a standard periapical radiograph (showing vertical and mesiodistal coordinates) paired with a cross-sectional occlusal radiograph (showing buccolingual depth). While primarily applicable to the mandible, it provides definitive spatial coordinates for surgical exodontia.